Process for manufacturing alcohols by oxidation of saturated hydrocarbons containing from 5 to 8 carbon atoms per molecule

ABSTRACT

THE PRESENT DISCLOSURE IS DIRECTED TO A PROCESS FOR CONVERTING SATURATED HYDROCARBON CONTAINING FROM 5 TO 8 CARBON ATOMS IN THE MOLECULE TO CORRESPONDING ALCOHOLS AND KETONES OF THE SAME NUMBER OF CARBON ATOMS WHICH COMPRISES CONTACTING SAID HYDROCARBONS IN THE LIQUID PHASE WITH AN OXIDIZING GAS BEING INTRODUCED AT A TEMCOMPOUND, SAID OXIDIZING GAS IN THE PRESENCE OF A BORON PERATURE BETWEEN ABOUT 100 TO 220*C., HYDROLYSING THE REACTION PRODUCT AND SEPARATING THE OBTAINED ALCOHOLS AND KETONES, SAID OXIDIZING GAS CONTAINING A MIXTURE OF ABOUT AIR AND A VAPOR OF THE HYDROCARBON TO BE OXIDIZED WHICH HAS BEEN PRELIMINARY PREHEATED TO A TEMPERATURE OF ABOUT 140 TO 190*C.

United States latent C) PROCESS FOR MANUFACTURING ALCOHOLS BY OXIDATIONOF SATURATED HYDROCARBONS CONTAINING FROM 5 TO 8 CARBON ATOMS PERMOLECULE Jacob Alagy, La Celle-Saint-Cloud, Christian Busson,Rueil-Malmaison, and Bernard Cha, Chatou, France, assignors to InstitutFrancais du Petrole, des Carburants 'et Lubrifiants, Rueil-Malrnaison,France N Drawing. Filed May 16, 1967, Ser. No. 638,719 Claims priority,application France, May 25, 1966,

- 62,988; Jan. 18, 1967, 91,680

Int. Cl. C07c 29/12, 45/02 US. Cl. 260-586 AB 6 Claims ABSTRACT OF THEDISCLOSURE The present disclosure is directed to a process forconverting saturated hydrocarbons containing from to 8 carbon atoms inthe molecule to corresponding alcohols and ketones of the same number ofcarbon atoms which comprises contacting said hydrocarbons in the liquidphase with an oxidizing gas in the presence of a boron compound, saidoxidizing gas being introduced at a temperature between about 100 to 220C., hydrolysing the reaction product and separating the obtainedalcohols and ketones, said oxidizing gas containing a mixture of air anda vapor of the hydrocarbon to be oxidized which has been preliminarypreheated to a temperature of about 140 to 190 C.

It is known that the oxidation of linear or cyclic saturatedhydrocarbons, in liquid phase, in the presence of a boric acid (forexample ortho-, metaor pyro-boric acid), boric anhydride, a boric esteror an equivalent boron compound, provides for boric esters of thealcohols corresponding to said hydrocarbons.

. Oxygen is usually emplyed at a concentration of 1 to 25% in admixturewith an inert gas such as nitrogen.

For example, oxidizing cyclohexane, under these conditions; provides fora cyclohexy borate. The oxidizable hydrocarbons are essentially alkanesand cycloalkanes which contain from 5 to 8 carbon atoms per molecule,for example hexane, heptane, octane, isooctane, cycloheptane,cyclooctane, methylcyclohexane and dimethycyclohexanes (ortho-, meta-,para-).

The oxidation temperature is usually comprised between 100 and 220 C.preferably between 140 and 190 C., the pressure being suflicient tomaintain a liquid phase, for example between 1 and 40 atmospheres.

This invention relates to a process of this kind wherein, by hydrolysisof the reaction product, before or after having separated a part or thewhole of the non-converted hydrocarbon, there is recovered boric acideither directly in the solid state or an aqueous solution which may besubmitted to crystallization, as well as an organic phase containing therequired alcohol having the same number of carbon atoms as the oxidizedhydrocarbon usually with a minor'amount of corresponding ketone.

As hydrolysis agent, there is used for example water or themother-waters of boric acid crystallization. The amount of used water isat least the stoichiometrical amount for the hydrolysis reaction; as anaverage there is used from 0.1 to 2 parts by volume of aqueous phase perpart by volume of liquid efiluent from the oxidation zone, and theoperating temperature is usually between 20 and 170 C. approximately.

The non-converted hydrocarbon may be recycled.

The recovered solid boric acid (essentially orthoboric acid) may be usedagain in a new oxidation operation, preferably after dehydration, so asto be at least in part under the form of alower hydrate of boric acid.

The process results into increased yields of alcohols and ketones.

This invention also relates to several improvements to the aboveprocess, which improvements may be used alone or as variouscombinations.

The process of this invention consists of using an oxidizing gascontaining oxygen and vapor of the hydrocarbon to be oxidized, forexample as an intimate mixture of oxygen, nitrogen and vapor of thehydrocarbon to be oxidized.

Preferably this mixture must be warm, for example at a temperature ofabout to 220 C., when it is introduced into the reactor.

Also for preparing the mixture, it is preferred to warm the nitrogenand/or oxygen gas, for example at about -190 -'C., before admixing thesame with the hydro carbon vapor.

If this is not done, there occurs the risk that the hydrocarbon bepartially condensed, which results into pressure drops in the pipes anda non-selective oxidation of this hydrocarbon.

According to a preferred embodiment which further improves the process,the nitrogen-oxygen mixture is saturated only partly with vapor ofhydrocarbon to be oxidized; the saturation rate is advantageouslycomprised between 20 and 90%, preferably between 30 and 55%. Thesaturation rate S, at a given temperature, is the ratio between thepartial pressure p of the hydrocarbon in the oxidizing mixture and thesaturating vapor pressure of the hydrocarbon p at the same temperature.The latter is given by the constants tables.

On the other hand, p, is proportional to the concentration c of thehydrocarbon in the oxidizing mixture:

where P is the total pressure (p is at most equal to p whence:

Usually the best results are obtained for gaseous mixtures of oxygen,nitrogen and hydrocarbon containing by volume 214% oxygen, 33-70%nitrogen and 28-58% hydrocarbon, provided the above conditions ofsaturation are respected.

It was prior known to dilute air by means of an inert gas such as thegas impoverished in oxygen resulting from a previous oxidation, so as tobring its oxygen concentration to a value comprised between about 2 and15%.

This technique is relatively expensive in power for circulating andcompressing the recycle gas. Moreover if care is not taken to reheat andsaturate the recycle gas with hydrocarbon, an intense evaporation of thehydrocarbon results, in the oxidation zone, which obliges to furnishconsiderable amounts of heat to the oxidation reactor and causes localoverheating which are detrimental to the yield and aspect of theproducts.

The improvement, object of this invention, and which remedies to theabove defects, consists of feeding the reactor with an oxidizing gasconsisting of an intimate mixture of oxygen, nitrogen and vapor of thehydrothrough one or several injectors, through a distributor or anyequivalent means.

There is advantageously used, in the oxidizing mixture of thisinvention, a volumetric ratio of the vaporized hy- .drocarbon to themixture oxygen nitrogen comprised between 0.5/1 and 10/1.

It is essential to introduce oxygen, nitrogen and hydrocarbon vapor intothe reactor as a mixture as intimate as possible. On the contrary ifthere is introduced separately air on one side and hydrocarbon vapor onthe other side, which possibility is outside the scope of thisinvention, there is not obtained the high yields of this invention.

It seems that, in the process of the invention, the hydrocarbon vaporwhich is presents in each gas bulb limits the speed of diffusion ofoxygen towards the interface gasliquid of each bulb, which gives time tothe formed molecules of alcohol and ketone to be dispersed through theliquid phase before having borne an undesired thorough oxidation.

An explanation of the observed critical values with respect to thesaturation rate could be the following:

At the interface gas-liquid of each gaseous bulb considered as amicro-reactor, a complementary vaporization of hydrocarbon would takeplace, due to the exothermicity of the oxidation reaction. In this way,the local temperature of the liquid at the interface level remainssubstantially the same as the average temperature of the liquid.

Conversely if the nitrogen and the oxygen contained in the bulb arecompletely saturated with hydrocarbon vapor, the vaporization is no morepossible. There results an excessive overheating at the interfacegas-liquid of the bulb, which results into secondary reactions which aredetrimental to the obtainment of good yields.

This explains why it is desirable to have hydrocarbon vapor in each gasbulb and why, however, the amount of vapor must be preferably lower thanthe saturation value.

It must be understood that the process which is the object of thisinvention, may be used together with all known and compatible processesfor oxidizing saturated hydrocarbons in the presence of boron compounds.In particular, although this is less preferred, one may introduce inknown manner a part of the air necessary to the process either as suchor preferably after dilution by means of an inert gas, for example therecycle gas. One may also admix with the feed gas of this invention agiven amount of recycle gas, although this is less preferred.

The following Examples 1-7 illustrate the process of this inventionwhereas Example 1A is given by way of comparison.

EXAMPLE 1 In an autoclave of stainless steel of 4 liters capacity isintroduced a mixture of 1,800 grams of cyclohexane and 130 grams ofmeta-boric acid. The autoclave is provided with a blade stirrer and withinlet ducts for introduction of gas in the vicinity of the bottom of theapparatus. The autoclave is surmounted with a condenser and a decanterplaced on the circuit of the gas evacuation in order to allow removal ofwater formed in the reaction. The cyclohexane which has been condensedan separated from water is returned to the reaction vessel.

The temperature is brought to 165 C. and the pressure to 12 kg./cm. asabsolute pressure. The oxidizing gas consists of an intimate, previouslyformed mixture of air with cyclohexane vapor prior to its introductioninto the reaction vessel, the ratio by volume of the cyclohexane vaporto the air being equal to 1.5, which corresponds substantially to thecomplete saturation of this air.

The reaction is stopped when 60 liters of oxygen have been absorbed. Thereaction product is hydrolyzed by water at a temperature of 100 C., in aconventional manner.

The molar yield of cyclohexanol+cyclohexanone mixture with respect tothe converted cyclohexane is equal to 89% and the conversion rate ofcyclohexane attains 12.4%.

EXAMPL'E 1A The same apparatus as in Example 1 is used with the samestarting amounts of cyclohexanone and metaboric acid, the sametemperature and the same pressure.

EXAMPLE 2 Cyclohexane oxidation is carried out continuously in acylindrical vertical reaction vessel of stainless steel in which theliquid phase (i.e. cyclohexane containing in suspension metaboric acid)is maintained at C., the pressure prevailing inside the reaction vesselbeing of 10.5 kg./cm. The respective feeding rates of cyclohexane andmetaboric acid are of 50 liters per hour and 2 kg. per hour.

The bottom of the reaction vessel, of conical shape, is perforated withholes through which oxidizing gas is allowed to pass. This gas isobtained by admixing previously, air preheated to C., with cyclohexanevapor also brought to the same temperature. The mixture effected outsideof the oxidation reaction vessel, contains 57% by volume of cyclohexanevapor and 43 by volume of air, which corresponds to a saturation rate of70%.

The experiment lasts 50 hours. During this entire time the gaseousmixture is regularly injected into the reaction vessel. The analysis ofthe liquid outflow from the reaction vessel, after hydrolysis, showsthat the molar yield of mixture cyclohexanol+cyclohexanone is equal to92% and the conversion rate equal to 12%.

EXAMPLE 3 The experiment described in Example 2 is repeated under thesame operating conditions except that air at the ambient temperature isadmixed with the stream of cyclohexane, vaporized at 175 C.

All other conditions being identical to those of Example 2, it isobserved that the pressure drop of the gaseous mixture between the inletduct therefor and the reaction zone is increased; after hydrolysis, themolar yield of cyclohexanol-l-cyclohexanone is only 89% and theconversion rate equal to 10.5%.

This shows why it is preferred to prepare the oxidizing mixture by meansof preheated oxygen and nitrogen.

EXAMPLE 4 Example 2 is repeated with different saturation rates of theoxidizing gas in cyclohexane vapor. The following results are obtained:

Percent Molar Conver- Saturation rate yield sion EXAMPLE 5 The samereaction vessel is used as in Example 2. The oxidation is carried outcontinuously at 165 C. under 10 kg./cm. The liquid cyclohexane rate is50 liters perhour and that of boric acid is 2.2 kg./hour.

The oxidizing mixture consists of 4% oxygen, 68% nitrogen and 28%cyclohexane vapor (by volume), which corresponds to a saturation rate ofabout 40% of the mixture oxygen-nitrogen by means of hydrocarbon vapor.

After hydrolysis, the following results are obtained: yield ofcyclohexanol+cyclohexanone mixture, 92.25%; conversion rate, 12.30%.

EXAMPLE 6 Example 5 is repeated with the same operating conditionsexcept that the saturation rate of the oxidizing mixture oxygen-nitrogenwith cyclohexane vapor is about Example 5 is repeated with the samesaturation rate of the hydrocarbon vapor, however, with differenthydrocarbons. The following results are obtained:

Percent Conver- Molar sion Hydrocarbon yield rate Methyleyclopentane 88.1 12. 5 n. Hexane 89.2 12.2 Cyelooctane- 92. 1 11. 5

What is claimed is:

1. A process for converting saturated hydrocarbons containing from 5 to8 carbon atoms in the molecules to corresponding alcohols and ketones tothe same number of carbon atoms which comprises contacting saidhydrocarbons in the liquid phase With an oxidizing gas in the presenceof a boron compound, said oxidizing gas being introduced at atemperature between about 100 to 220 C., hydrolyzing the reactionproduct and separating the obtained alcohols and ketones, said oxidizinggas containing a mixture of air and a vapor of the hydrocarbon to beoxidized, said mixture containing by volume, 2-14% oxygen, 33-70%nitrogen and 2858% said hydrocarbon vapor, and said air and hydrocarbonvapor being preliminarily and separately preheated, before beingadmixed, to a temperature of about 140 to 190 C.

2. Process according to claim 1 wherein the saturation rate of theoxidizing gas with the vapor of the hydrocarbon to be oxidized, at theinlet of the oxidation zone, is between 20 and 3. Process according toclaim 2 wherein the saturation rate of the oxidizing gas with the vaporoi hydrocarbon to be oxidized at the inlet of the oxidation zone, isbetween 30 and 55% 4. Process according to claim 1, wherein thehydrocarbon is cyclohexane.

5. Process according to claim 1, wherein the boron compound is boricanhydride, a boric acid or a boric ester.

6. A process for converting saturated hydrocarbons containing from 5 to8 carbon atoms in the molecules to corresponding alcohols and ketones orthe same number of carbon atoms which comprises contacting saidhydrocarbons in the liquid phase With an oxidizing gas in the presenceof a boron compound, said oxidizing gas being introduced at atemperature between about to 220 C., hydrolyzing the reaction productand separating the obtained alcohols and ketones, said oxidizing gascontaina mixture of air and a vapor of the hydrocarbons to be oxidized,said oxidizing gas being characterized by a ratio by volume of thevaporized hydrocarbon to oxygen-l-nitrogen between 0.5 :1 and 10: 1, andsaid air and hydrocarbon vapor being preliminarily and separatelypreheated, before being admixed to a temperature of about to C.

References Cited UNITED STATES PATENTS 3,317,614 5/ 1967 Marcell 260632CB 3,274,254 9/1966 Seddon 260-586 B 1,947,989 2/1934 Hellthaler 260586B LEON ZITVER, Primary Examiner N. MORGANSTERN, Assistant Examiner US.Cl. X.R.

260597 'R, 617 H, 631 B, 632 CB

